1 . Field of the Invention
The present invention relates generally to discovering neighboring nodes in a network and protection of asynchronous transfer mode (ATM) traffic against Synchronous Optical Network (SONET) fiber cuts or other types of transmission media failures in a SONET Ring.
2 . Description of the Related Art
As a result of the expansion in data communication, there is an increasing demand for high quality transmission of various data such as computer data, facsimile data, voice data, animation data, etc. in a communication network. A broadband ISDN (B-ISDN) has been developed and standardized to be used with various interfaces for practical use as a communication network service capable of transmitting data at various speeds by processing collectively in an asynchronous mode both burst information and continuous information.
In the ATM network, data in different bands are contained in a fixed length unit, which is called a "cell". In this system, as data are inserted in cells, various services can be offered where different transmission speeds are required. Thus, the transmission line can be used efficiently. In the ATM communication, user information is divided into a plurality of parts of appropriate length, each being added to a header to form a cell. A header part of each cell includes, for example, a virtual channel identifier (VCI), a virtual path identifier (VPI) and a payload or cell data. The VCI identifies a source user. The user information is typically multiplexed after a cell is generated, and then transmitted or switched to an ATM highway. Cell data are called "self-routing data" because the cell data are transmitted autonomously and indicate the destination or destinations of the cell data.
In the B-ISDN network, a synchronous optical network (SONET) format may be adopted as a transmission apparatus as disclosed in U.S. Pat. No. 5,251,204, wherein a number of ATM cells may be grouped and transmitted in a frame among slots.
In FIG. 1, a SONET 10 includes a SONET working ring 20 and a SONET protection ring 30. As shown in FIG. 1, the SONET working ring 20 may, for example, transmit ATM cells or data synchronously in a clockwise direction. The SONET working ring 20 is connected to a plurality of nodes A-D. Each of the nodes A-D may be connected to one or more work stations (not shown). If the SONET working ring 20 made of an optical fiber was cut or another media interruption occurred, due to a hardware failure for example, a node can obtain data from a SONET protection ring 30, which transmits the data in the counterclockwise direction, for example. However, since ATM cells, which are transmitted from one node to another node by way of the SONET working ring 20, may arrive earlier than the ATM cells transmitted by way of the SONET protection ring 30 or vice versa due to the number of intervening nodes and the congestion at each intervening node, it has not been possible to merely switch all of the nodes to accept the ATM cells from the SONET protection ring 30. Therefore, in the prior art ATM cells are unprotected in SONET networks.
A SONET ring network is not the only type of network containing a working path and protection path for transmitting data. There are several types of networks including full mesh, partial mesh, matrix, and hypercube. All of these networks have similar problems in protecting ATM cells.